Diesel Particulate Filter (DPF); How they work and why they cause problems.


The DPF looks similar to a traditional exhaust silencer but is mounted close to the engine. Inside is a complex honeycomb ceramic structure designed to filter the exhaust gases while minimising flow reduction (which would otherwise limit performance). By forcing the exhaust gases through the walls between the channels of the DPF, the particulate matter is deposited on the walls, so reducing the amount of air pollution. Once the DPF reaches a certain level of ‘Saturation’ it performs a regeneration cycle to burn off the particulate matter inside the filter.


A car which is primarily used for motorway use will generally run at warmer temperatures and therefore produce far less particulate matter than one used in a stop/start city environment. A vehicle used on the motorway is also going to be able to regenerate more often and effectively as it is in the perfect driving environment for the regeneration process to occur,

  • Vehicles used for short trips and low speeds produce more particle matter and do not often reach the conditions required to initiate automatic regeneration of the DPF; requiring manual intervention to clear the DPF system of the soot build up,
  • Larger diesel vehicles with low duty cycles (short trip, low speeds) will suffer particularly with soot build up in the DPF.


 Diesel Particulate Filter (DPF) regeneration (cleaning)


The Diesel Particulate Filter (DPF) indicator signifies your vehicle's DPF filter has not been regenerated (cleaned) and will require a manual / static regeneration. Once this service is indicated it is advisable to have the procedure carried out as soon as possible to avoid long term and possibly expensive damage to the filter.



Why does the DPF need regeneration / cleaning ?


The DPF filter traps carbon particles, filtering exhaust gases as they pass through and, like any filter, this must be regenerated (cleaned) to restore it to full operation. Under normal circumstances the regeneration process is carried out by the car itself when the engine management/emissions management system detects the DPF is in need of regeneration. However Diesel vehicles used mainly for short journeys do not provide the system sufficient opportunity to regenerate the DPF resulting in a fault developing. This fault is indicated by the DPF / engine management fault indicator illuminating and/or a fault message on vehicles equipped with display.


What is DPF regeneration / cleaning ?


When a fault develops with the DPF filter, indicating manual regeneration is required this is completed in combination of the workshop and driving the vehicle. Using our service computer we first tell the car to initiate the DPF regeneration process and then run the car at load - either by driving the car on the road, During the regeneration process sufficient heat must be generated for long enough for the regeneration to complete.



What if I don't have the DPF Regenerated ?


Once the Engine Management Fault / DPF Fault Indicator has illuminated this indicates the DPF has not been regenerated through the normal driving range of the vehicle and requires manual/static regeneration. Failure to have the regeneration completed at this stage could render the filter itself beyond repair and require complete replacement. A DPF that reaches 90% or approx. 45 grams full will be beyond regeneration and require complete replacement. Depending on your vehicle make and model a failed Diesel Particulate Filter can be very expensive.


Why you cannot manually regenerate the Diesel Particulate Filter yourself.


If you use your diesel vehicle for mainly short trips and the engine management light illuminates it maybe possible to have the car enter regeneration itself by simply using the vehicle over a long distance. However this is not recommended and is seldom successful because;

  • You cannot guarantee the vehicle will enter regeneration mode (we use our diagnostic equipment to tell the car to enter regeneration mode)
  • You must create significant engine load / heat to enable AND complete the regeneration cycle
  • The fault indicator will not switch off typically without the fault code being cleared (you may never know the DPF has been regenerated!)

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